The present invention relates to the art of stack gas scrubbing, and more particularly to the selective removal of acidic impurities from a stream of mixed gases, i.e., sulfur oxides from flue gases. The term "flue gas" or "stack gas" as used herein refers to the hot gaseous waste mixture resulting from various sulfur oxide producing processes, i.e., stack gas from smelters or coal-fired electric power plants.
With growing dependence on coal as an energy source for the generation of electric power, the removal of sulfur compounds from flue gases is becoming a significant problem. Electric utilities are currently meeting air quality standards by burning low sulfur western coal. The cost of shipping this coal is very high, forcing electrical utilities in the east to install flue gas desulfurization systems to enable the plants to burn eastern coal of higher sulfur content. The requirements of a flue gas desulfurization process are twofold; the technique of the process must be highly effective for the removal of SO.sub.2 and SO.sub.3 from flue gases, and the system must be highly reliable to enable it to remain on line almost continuously. In addition, it is desirable that a flue gas desulfurization process be economical with respect to the use of water and the disposal of waste scrubbing medium.